1. Field of the Invention
The present invention relates to a rotor of an electric motor having a structure for attaching magnets securely to a circumferential surface of an iron core, and to a manufacturing method thereof.
2. Description of the Related Art
In a rotor of an electric motor in which magnets are arranged on an outer circumferential surface of an iron core, adhesive is used in order to attach the magnets to the core. However, if adhesive is used, the amount and hardening of the adhesive have to be managed, so that cost tends to increase and quality control will be difficult. Further, not only is a cleaning step required to clean the surface of the core before adhesive is applied thereto, but an additional step is required to remove excess adhesive after the adhesive is applied. Moreover, magnets attached by means of adhesive make it difficult to ensure that the fixing structure has enough strength to withstand torque and centrifugal force during rotational movement of the electric motor.
A rotor in which a protective pipe is provided so as to surround the outer circumferences of magnets so that an inner surface of the protective pipe and an outer surface of the magnets are brought into close contact with each other has been known (see JP-A-2009-106065). A rotor in which resin is filled in a gap defined between a protective pipe and a core has also been known (JP-A-2009-95200). However, in the structure in which resin is simply filled in the gap between the protective pipe and the core, it is difficult to ensure that the magnets are stably brought in close contact with the core. As a result, mechanical or magnetic balance cannot be maintained, and therefore, rotor balance is impaired. There also arises a problem due to cogging.
Therefore, there is a need for a rotor of an electric motor that allows magnets to be reliably and stably fixed to an outer circumferential surface of a core without use of adhesive, and a manufacturing method for manufacturing such a rotor of an electric motor.